A novel ultrafast all-optical switching based on metal-insulator-metal nanoplasmonic waveguide with a Kerr nonlinear resonator is proposed and investigated numerically. With the finite-difference time-domain simulations, it is demonstrated that an obvious optical bistability of the signal light appears by varying the control-light intensity, and an excellent switching effect is achieved. This bistability originates from the intensity-dependent change induced in the dielectric constant of Kerr nonlinear material filled in the nanodisk resonator. It is found that the proposed all-optical switching exhibits femtosecond-scale feedback time.

A novel and simple plasmonic filter based on metal-insulator-metal plasmonic waveguides with a nanodisk resonator is proposed and investigated numerically. By the resonant theory of disk-shaped nanocavity, we find that the resonance wavelengths can be easily manipulated by adjusting the radius and refractive index of the nanocavity, which is in good agreement with the results obtained by finite-difference time-domain (FDTD) simulations. In addition, the bandwidths of resonance spectra are tunable by changing the coupling distance between the nanocavity and waveguides. This result achieved by FDTD simulations can be accurately analyzed by temporal coupled mode theory. Our filters have important potential applications in high-density plasmonic integration circuits.

Topological photonics has recently been proved a robust framework for manipulating light. Active topological photonic systems, in particular, enable richer fundamental physics by employing nonlinear light-matter interactions, thereby opening a new landscape for applications such as topological lasing. Here we propose an all-dielectric topological insulator laser scheme in telecommunication region based on semiconductor cavities formed by topologically distinct Kagome photonic crystals. Our theoretical results show that the proposed planar semiconductor Kagome lattice can lift degeneracy with geometrical perturbation and open broad photonic bandgaps, and valley-dependent edge states and topologically robust transport with subwavelength scale confinement are observed at the edge of the perturbed Kagome lattices with distinct valley Chern numbers. An interesting feature of the Kagome lattices is that it supports two different types of valley Hall edge modes, which enables the coexistence of high Q ring-resonator modes and lossy Fabry-Pérot resonator modes in the proposed topological cavities. Moreover, we explore pumping and lasing dynamics of the topological cavities by means of a four-level two-electron model and demonstrate that this model offers a powerful platform to investigate non-Hermitian topological laser cavities with arbitrary geometry. The proposed topological semiconductor scheme provides a new route to study non-Hermitian topological photonics and to develop integrated topological systems for robust light generation and transport.